1. Field of the Invention
The present invention relates to the field of optical disk drives. More specifically, it relates to an analog signal operational large scale integrated circuit (LSI) for a multi-beam pick-up device which can be used to process signals from two or more kinds of pick-up devices, each of the pick-up devices having a different arrangement of photo detectors.
2. Description of the Related Art
In the conventional optical disc drive for recording, reproducing and erasing information on a CD-R disc and a CD-RW disc, a pick-up device which receives a laser ray has a plurality of photo detectors. The pick-up device receives output signals from the photo detectors in an operation circuit and calculates a reproducing signal (RF), a focusing error signal (FE), a tracking error signal (TE), a lens positional signal (LP), a track cross signal (TC), a push-pull signal and so on. The pick-up device uses a photo diode (PD) as a photoelectric converter. Since output impedance of the photo diode is high, if the transmission line is long, its measurements are easily influenced by outside noise and the floating capacity of the signal line. Therefore, an Optical Element Integrated Circuit (OEIC) is formed in which a plurality of photo detectors are arranged in a plane and the PD output current signals are converted into an output voltage signal.
With regard to the arrangement of the plurality of photo detectors of the pick-up device, at least two different photo detector arrangements for pick-up devices are often used. Based upon the output signals of respective photo detectors of the pick-up devices, the above mentioned signals (i.e., the reproducing signal (RF), focusing error signal (FE), tracking error signal (TE), lens positional signal (LP), track cross signal (TC), push-pull signal, etc.) are arrived at by arithmetic operation. For example, in both pick-up devices, eight photo detectors are provided (A, B, C, D, E, F, G, H), and they are arranged in a different pattern in each pick-up device. For example, one pick-up device calculates the focusing error signal by the operational expression xe2x80x9c{(A+D)xe2x88x92(B+C)}/(A+B+C+D),xe2x80x9d the other pick-up device calculates the focusing error signal by the operational expression xe2x80x9c(Axe2x88x92B)/(A+B).xe2x80x9d Other signals are calculated by using different expressions.
For each pick-up device having a different photo detector arrangement, its respective calculating circuit is also different. Such calculating circuits generally comprise LSIs. Since, as described above, a special calculating circuit is formed for respective pick-up devices, according to its specific pick-up methods, it is necessary to provide a specific LSI for each pick-up device.
OEIC photo detectors have approximately the same gain. Therefore, LSIs having different gains, in response to OEIC gain levels, must be manufactured.
In accordance with an embodiment of the present invention, an analog signal operational LSI for use in an optical disc apparatus is provided. The analog signal operational LSI has switching circuits which are provided with a calculating circuit for calculating servo signals (e.g., focusing signal, tracking signal, etc.) based on output signals received from a plurality of photo detectors and from an input portion of the LSI. The configuration of the switching circuits are variable such that the calculating of the servo signal of the LSI can adapt to the differing calculating expressions of each respective pick-up device with which the LSI can be used. That is, since there are two or more kinds of pick-up devices, each having a different arrangement of its photo detectors, so too must the switching circuits be different which receive output signals from the pick-up devices. The LSI provides the proper servo signals no matter which pick-up device it is used with.
In accordance with an embodiment of the present invention, a gain changing circuit is also provided. An output portion of the gain changing circuit is coupled to the analog signal operational LSI. Also, in accordance with an embodiment of the present invention, the gain changing circuit has two steps of reproducing, recording and erasing for each disc.
The present invention provides for a single LSI which can adapt to two differing pick-up devices by changing the switching circuit. Furthermore, even though there is no gain changing function within a pick-up device the present invention properly utilizes the output signals of each pick-up device and easily adjusts for variances within each disc.